When power electronics modules or PEBBs (Power Electronics Building Blocks) are integrated into systems, such as converters for example, they are usually screwed to supports in a metal cabinet as a support structure and manually connected to power lines, a cooling system and signal lines. In the majority of converters, a power electronics module comprises a connection point at which said power electronics module is connected to ground potential, either directly or by means of an electrical line.
When a power electronics module is intended to be used in such a way that a connection to ground potential of this kind is not expedient (as is often the case in a multilevel converter for example) and is intended to be provided with a connection to an electrical potential which differs from ground potential, the power electronics module can be equipped with a housing which is composed of insulating material or with field-homogenizing elements which are fitted within the cabinet by means of insulators at a sufficiently large distance from the cabinet and other surrounding components. In this case, the cabinet is normally at ground potential.
In the majority of water-cooled power electronics converters, the main system pipes for coolant are at ground potential and the heat sinks which are at a different electrical potential are connected to the main system pipes by means of insulating pipes (for example rubber or plastic). When the heat sinks are at a different electrical potential, an electric current generally flows through the cooling water.
Some components in the coolant circuit begin to corrode when they are exposed to this electrolysis current for a relatively long time. In certain empirical studies, safety levels have been defined for different metal materials, the corrosion rate at said safety levels being low enough in order to ensure that no problems can occur during the service life of the product. Typical measures for reducing the electrolysis currents and achieving these safety levels comprise deionized water and adapting the geometry of the insulating pipes.
Deionized water, which is optionally mixed with glycol in order to prevent freezing, has a very low level of conductivity. The conductivity of the water can also be monitored, and the conductivity can be kept low by continuous removal of ions from the liquid.
Furthermore, the length of the insulating pipes can be increased and/or the diameter of said insulating pipes can be reduced in order to increase the resistance in these sections of the water circuit and therefore to lower the electrolysis currents to the corresponding safety level.
However, in some cases, it is not expedient or possible to correspondingly change the geometry of the insulating pipes. For example, at certain voltage levels, it would be necessary to increase the pipe lengths in such a way that the pressure would drop too much. In addition, the available installation space can limit the length of the pipes.